Field of the Disclosure
The present disclosure relates generally to signal processing and, more particularly, to digital vector signal processing.
Description of the Related Art
Temporal alignment of signals is crucial to many aspects of wireless communication systems. For example, time alignment of input signals and feedback signals reduces cross-channel interference in the power amplifiers implemented in base stations and user equipment to amplify signals for transmission over the air interface. The power amplifiers are typically operated in a non-linear mode to achieve higher efficiency and reduce power consumption. However, the non-linear response of the power amplifier increases the frequency bandwidth of the output signal (relative to the frequency bandwidth of the input signal), which increases interference between different radio frequency carriers.
Digital predistortion can compensate for the effects of the non-linear power amplifier on the output signal by applying an inverse distortion to the input signal. The inverse distortion is determined by comparing the input signal to time-aligned feedback from the output of the power amplifier. Time alignment is conventionally performed using polynomial based interpolators such as a Farrow structure. Errors or inaccuracies in the time alignment of the input and feedback signals reduce the effectiveness of predistortion. The precision of the time alignment can be increased by increasing the degree or the number of taps implemented by the interpolator, e.g., the Farrow structure. However, polynomial interpolation is computationally intensive and improving the accuracy of the interpolators requires increasing the computation time and power consumption, which is not feasible for many current and future products.